In the class of hearing aid systems generally referred to as implantable hearing instruments, some or all of various hearing augmentation componentry is positioned subcutaneously on or within a patient's skull, typically at locations proximate the mastoid process. In this regard, implantable hearing instruments may be generally divided into two sub-classes, namely semi-implantable and fully implantable. In a semi-implantable hearing instrument, one or more components such as a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit an audio signal to implanted components such as a transducer. In a fully implantable hearing instrument, typically all of the components, e.g., the microphone, signal processor, and transducer, are located subcutaneously. In either arrangement, an implantable transducer is utilized to stimulate a component of the patient's auditory system (e.g., ossicles, oval window and/or the cochlea).
Implantable hearing instruments are typically classified by the portion of the ear for which they are operative to stimulate. For instance, middle ear hearing instruments are designed to stimulate the auditory components of the middle ear, which includes the tympanic cavity, the tympanic membrane (eardrum) and three small bones called the auditory ossicles. The tympanic cavity is an air filled space that separates the external ear (ear canal) and the inner ear (cochlea). In a healthy ear, the ossicles bones (malleus, incus and stapes) form a bridge or ossicular chain across the tympanic cavity connecting the eardrum to the inner ear/oval window and function to transmit vibrations between these auditory components.
Known implantable hearing aid devices include those which utilize implanted electromechanical transducers positioned within the middle ear (i.e., middle ear transducer) for stimulation of the ossicular chain and/or oval window (see e.g., U.S. Pat. No. 5,702,342). Middle ear transducers typically include a vibratory actuator that interfaces with and stimulates the ossicular chain of the patient via physical engagement. In this regard, one or more bones of the ossicular chain are made to mechanically vibrate, which causes the ossicular chain to stimulate the cochlea through its natural input, the oval window.
As may be appreciated, the utilization of an implantable hearing aid actuator of the above-noted nature entails surgical positioning of the vibratory actuator. Such positioning is typically within the mastoid process of a patient's skull and requires the insertion of the vibratory actuator through a hole formed in the mastoid process and extending into the tympanic cavity, which is also sometimes referred to as the ‘attic.’ Due to the position of the ear canal, the hole formed through the mastoid process generally intersects the tympanic cavity in a region of the attic where the incus and malleus are found. In this case, the vibratory actuator may be coupled to the ossicles during mounting and positioning of the transducer within the patient. In one example, such coupling may occur via a small aperture formed in the incus bone.